April 6, 2019

Buy a (real) Book! Beej’s Guide to Network Programming (online and for download) This is a beginner’s guide to socket programming with Internet sockets . Beej’s Guide to Network Programming. Note for Windows Programmers. I have a particular dislike for Windows, and encourage you to try Linux, BSD. Beej’s Guide to Network Programming has been one of the top socket programming guides on the Internet for the last 15 years, and it’s now for the first time.

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Except to remember that if you’re using Windows and Winsock that you should call closesocket instead of close.

The maximum lengths are: If you are connect ing to a remote machine and you don’t care what your local port is as is the case with telnet where you only care about the remote portyou can simply call connectit’ll check to see if the socket is unbound, and will bind it to an unused local port if necessary. Unfortunately, the purpose of a firewall is to prevent people outside the firewall from connecting to machines inside the firewall, so allowing them to do so is basically considered a breach of security.

Read it anyway, just for kicks. There are some obvious exceptions, but they’re few and far between. Well, it used to be a union, but now those days seem to be gone. In particular, gethostbyname doesn’t work well with IPv6. I’ve already done this nasty business, and I’m dying to share the information with everyone!

Beej’s Guide to Network Programming

Lots of places have a firewall that hides the network from the rest of the world for their own protection. For instance, with IPv4, you might have But enough of the starry-eyed future—we’re stuck in the bit present. You’re hitting the MTU—the maximum size the physical medium probramming handle.

Basically, you’ll want to convert the numbers to Network Byte Order before they go out on the wire, and convert them to Host Byte Order as they come in off the wire. Stream sockets are reliable two-way connected communication streams. Well, incoming connections are going to wait in this queue until you accept them see below and this is the limit on how many can queue up.


If you set the parameter timeout to NULL, it will never timeout, and will wait until the first file descriptor prograkming ready. I don’t know what that does, exactly, but some people seem to need it. Be aware that a hole in the firewall is nothing to be taken lightly. Except for one more tiny detail that I’ve mentioned many times in the neteork Having the server execute what the client says is like giving remote shell access and people can do things to your account when they connect to the server.

If you’re sending chat messages, TCP is great; if you’re sending 40 positional updates per second of the players in the world, maybe it doesn’t matter so much if one or two get dropped, and UDP is a good choice. If listener doesn’t respond, it could be because it’s bound to an IPv6 address. I remember being provided Beej’s Guide and it being indespensable.


What if you don’t want to connect to a remote host. It allows you to cut off communication in a certain direction, or both ways just like close does. The advantage of this method is that you only need a buffer large enough for one packet, while the disadvantage is that you need to call recv at least twice to get all the data. Run listener on some machine, then run talker on another. It’s also used in host name lookups, and service name lookups.

This is cool because your code can be IP version-agnostic.

In this example, s is the socket you nehwork to send the data to, buf is the buffer containing the data, and len is a pointer to an int containing the number of bytes in the buffer. This is the variable that holds error information for a lot of system calls. You don’t even have to run the server this time!

See the sendall function implementation for details. If it arrives, the data within the packet will be error-free. See the section on blocking for more details. Aw man I used his wonderful guides and examples all the way from middle school up through uni; I owe him a lot of my success to this day!


I first went through this in my early high school years back in or so and wrote a very basic chat program that could be used on our school network. The length is stored in Network Byte Order, of course. What is a socket? My favorite solution to this involves a goto statement. All this client does programning connect to the host you specify on the command line, port In the book ” The Practice of Programming ” by Kernighan and Pike, they implement printf -like functions called pack and unpack that do exactly this.

One cannot go wrong. In short, no changes are necessary to any of the code to make it run on a single non-networked machine! The servname parameter is basically the port number.

Beej’s Guide to Network Programming

Notice that this has the added benefit of allowing your program to do something else while it’s connecting, too. Netwwork you’re only getting one single connection ever, you can close the listening sockfd in order to prevent more incoming connections on the same port, if you so desire.

You can either wait for it to clear a minute or soor add code to your program allowing it to reuse the port, like this:. For one thing, you can’t use close to close a socket—you need to use closesocketinstead. If you just want any old IP address for this host yeah, they can have more than one just use this field. You also have to tell your compiler to link in the Winsock library, usually called wsock You probably have to encapsulate remember that from the progarmming encapsulation section way back there at the beginning?

Well, we’re finally here.